He left soon after to join WalMart as head of its China operations and had been running WalMart's entire Asian operations since June.

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"Greg is one of the many world-class retailers to have worked with Woolworths over the years," Mr O’Brien said. "Woolworths has long had a close relationship with Walmart and we look forward to continuing this into the future."

New Zealand-born Mr Foran served in several senior roles at Woolworths during his 10 years with the company, including managing director of supermarkets, liquor and petrol, general manager of BIG W and general manager of Dick Smith.

He joins WalMart's US operations at a difficult time. Same-store sales have fallen for five consecutive quarters.

Woolworths announced a significant executive departure on Friday as Julie Coates, a potential CEO candidate, suddenly quit the retailer just 10 months into leading a crucial billion dollar project to transform the company's intricate supply and logistics operations.

It leaves the project, dubbed Mercury 2, for the moment without a clear leader at a time when bricks-and-mortar retailers such as Woolworths are scrambling to cope with the shift to online shopping.

Woolworths said Ms Coates, director of business transformation, had decided to "pursue other career opportunities".

Ms Coates, a 12-year veteran of the company, was the boss of its merchandise chain Big W between 2008 and 2013 and sits on the board of Woolworths' loss-making hardware joint venture Masters.

In October Ms Coates took on the business transformation role, establishing the strategy and road map to overhaul its back-of-store operations that was expected to be a 10-year process and cost as much as $1 billion.

Woolworths heralded it as the next phase of its supply chain innovation and placed Ms Coates at the centre of a powerful working group that oversaw logistic operations that shifted more than 20 million cartons of goods each week and 3000 truck movements a day.

Mercury 2 is set to touch all of Woolworths' retail brands including its supermarkets, big-box liquor chain Dan Murphy's, Big W and Masters.

It is unclear who will replace Ms Coates as the leader of Mercury 2, and if a new project leader will carry on with her strategy or present a new plan to the Woolworths board.

A spokeswoman for Woolworths said the Mercury 2 project was not reliant on Ms Coates and would be delivered by many people within the business.

Woolworths said Ms Coates would remain on the Masters board until the end of the year.

Mr O’Brien thanked Ms Coates for her "significant contribution to the company over many years" and wished her well in her future career.